Vacuum pump, vacuum exhaust device, and method of operating vacuum pump

ABSTRACT

[Object] To provide a vacuum pump, a vacuum exhaust device, and a method of operating a vacuum pump that are capable of achieving a stable exhausting operation without causing a step-out. 
     [Solving Means] Provided is a method of operating a vacuum pump including a rotor ( 21, 22 ), a drive motor ( 35 ), and a magnetic coupling ( 50 ) configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value (Th 1 ). The method includes detecting a load torque of the drive motor ( 35 ). The number of revolutions of the drive motor ( 35 ) is increased when the load torque is equal to or smaller than a second threshold value (Th 2 ) that is smaller than the first threshold value (Th 1 ). The number of revolutions of the drive motor ( 35 ) is reduced when the load torque exceeds the second threshold value (Th 2 ) and is equal to or smaller than the first threshold value (Th 1 ).

TECHNICAL FIELD

The present invention relates to a vacuum pump in which a magnetic coupling is used for transmission of a driving force, a vacuum exhaust device, and a method of operating a vacuum pump.

BACKGROUND ART

A mechanical booster pump is a positive-displacement-type vacuum pump that transfers gas from an intake port to an exhaust port by rotating two cocoon-shaped rotors, which are arranged in a casing, in a synchronized manner in opposite directions. In the mechanical booster pump, the rotors do not come into contact with each other and each rotor and the casing do not come into contact with each other. Therefore, the mechanical booster pump causes less mechanical loss and has an advantage that energy required for driving can be reduced as compared to a vacuum pump having a large frictional work, such as an oil-rotary vacuum pump.

The mechanical booster puma does not require lubricating oil within a pump chamber that accommodates both of the rotors, and therefore contamination of a vacuum due to the oil is less caused. On the other hand, in terms of operation of the pump, rotational phases of both of the rotors and the center of an axis of each rotor are constantly correctly maintained. Therefore, lubrication is required for gears for rotating the rotors in a synchronized manner, bearings for supporting rotation shafts of the rotors, and the like. For that reason, the lubricating oil is retained in a gear chamber that accommodates the gears, and each part is lubricated at a time of operation.

However, there is a possibility that air is leaked from the casing to a motor chamber that accommodates a motor due to an increase in pressure of the exhaust port or oil is leaked from a shaft seal. Such a problem is liable to occur in an early stage of the driving of a pump, particularly in the case where a vacuum chamber is exhausted from atmospheric pressure to a vacuum. In this regard, there is known a vacuum pump that ensures airtightness between the inside of the casing and the motor chamber by partitioning the inside of the casing and the motor chamber and coupling the motor and the rotor with a magnetic coupling (see, for example, Patent Document 1 below).

Patent Document 1: Japanese Patent Application Laid-open No. Hei 06-185483

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, in a mechanical booster pump having a magnetic coupling structure, a phenomenon that a magnetic connection between a motor and a rotor is released when a load torque of the motor is excessively large (step-out) is caused. When the step-out is caused, a proper pump operation is disabled any more, and therefore the pump operation is required to be stopped once and then rebooted. Therefore, if the step-out occurs repeatedly, an exhausting operation of an exhausted system requires a lot of time.

In view of the circumstances as described above, it is an object of the present invention to provide a vacuum pump, a vacuum exhaust device, and a method of operating a vacuum pump that are capable of achieving a stable exhausting operation without causing a step-out.

Means for Solving the Problem

In order to achieve the above object, according to an embodiment of the present invention, there is provided a vacuum pump including a pump unit, a drive unit, a magnetic coupling, and a controller.

The pump unit includes a pump chamber including an intake port and an exhaust port, and a rotor that is arranged in the pump chamber and transfers gas from the intake port to the exhaust port.

The drive unit includes a motor chamber adjacent to the pump chamber, and a drive motor that is arranged in the motor chamber and rotates the rotor.

The magnetic coupling includes a partition member, a first magnet, and a second magnet. The partition member airtightly partitions the pump chamber and the motor chamber. The first magnet is attached to the rotor. The second magnet is attached to the drive motor and is magnetically connected to the first magnet via the partition member. The magnetic coupling is configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value.

The controller includes a detection section and a revolution control section. The detection section detects a load torque of she drive motor. The revolution control section controls the number of revolutions of the drive motor. The controller increases the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reduces the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.

According to an embodiment of the present invention, there is provided a vacuum exhaust device including a first vacuum pump, a second vacuum pump, and a controller.

The first vacuum pump includes a pump chamber, a rotor, a drive motor, and a magnetic coupling. The pump chamber includes an intake port and an exhaust port. The rotor is arranged in the pump chamber and transfers gas from the intake port to the exhaust port. The magnetic coupling is configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value.

The second vacuum pump exhausts the gas transferred to the exhaust port.

The controller includes a detection section and a revolution control section. The detection section detects a load torque of the drive motor. The revolution control section controls the number of revolutions of the drive motor. The controller increases the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reduces the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.

According to an embodiment of the present invention, there is provided a method of operating a vacuum pump including a rotor, a drive motor, and a magnetic coupling configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value.

The method includes detecting a load torque of the motor.

The number of revolutions of the drive motor is increased when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value.

The number of revolutions of the drive motor is reduced when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A schematic configuration diagram of a vacuum exhaust device according to an embodiment of the present invention.

[FIG. 2] A schematic cross-sectional view of a vacuum pump according to the embodiment of the present invention.

[FIG. 3] A cross-sectional view showing details of a pump unit of the vacuum pump.

[FIG. 4] A flowchart for describing a method of operating the vacuum pump.

[FIG. 5] A timing chart showing a relationship between a load torque and the number of revolutions of the motor of the vacuum pump.

[FIG. 6] Results of an experiment showing a change in the number of revolutions of the vacuum pump and temporal changes in pressure on an intake side and on an exhaust side.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

According to an embodiment of the present invention, there is provided a vacuum pump including a pump unit, a drive unit, a magnetic coupling, and a controller.

The pump unit includes a pump chamber including an intake port and an exhaust port, and a rotor that is arranged in the pump chamber and transfers gas from the intake port to the exhaust port.

The drive unit includes a motor chamber adjacent to the pump chamber, and a drive motor that is arranged in the motor chamber and rotates the rotor.

The magnetic coupling includes a partition member, a first magnet, and a second magnet. The partition member airtightly partitions the pump chamber and the motor chamber. The first magnet is attached to the rotor. The second magnet is attached to the drive motor and is magnetically connected to the first magnet via the partition member. The magnetic coupling is configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value.

The controller includes a detection section and a revolution control section. The detection section detects a load torque of the drive motor. The revolution control section controls the number of revolutions of the drive motor. The controller increases the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reduces the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.

In the vacuum pump, the drive motor transmits a rotational force to the rotor at a rotational torque equal to or smaller than the first threshold value. The first threshold value corresponds to a rotational torque at which the drive motor and the rotor can be rotated in a synchronized manner without causing a step-out of the magnetic coupling. The step-out of the magnetic coupling occurs when a rotational load of the rotor exceeds a rotational load of the drive motor. For example, a step-out is liable to occur when a pressure of the exhaust port (back-pressure) excessively rises at an initial time of the driving of the pump. The vacuum pump described above is intended to achieve a stable exhausting operation without causing the step-out of the magnetic coupling by setting the first and second threshold values for the load torque of the drive motor and controlling the number of revolutions of the drive motor in accordance with the magnitude of the detected load torque. Thus, for example, a stable exhausting operation from atmospheric pressure to a predetermined reduced-pressure atmosphere can be achieved.

The controller may put the drive motor into a free running state when the load torque exceeds the first threshold value. When the detected load torque exceeds the first threshold value, there is a high possibility that the magnetic coupling causes a step-out. In this regard, in the vacuum pump described above, when the load torque of the drive motor exceeds the first threshold value, the drive motor is put into a free running state where the excitation of the drive motor is blocked and the drive motor is rotated through inertia. Thus, the step-out state of the magnetic coupling can be resolved early.

According to an embodiment of the present invention, there is provided a vacuum exhaust device including a first vacuum pump, a second vacuum pump, and a controller.

The first vacuum pump includes a pump chamber, a rotor, a drive motor, and a magnetic coupling. The pump chamber includes an intake port and an exhaust port. The rotor is arranged in the pump chamber and transfers gas from the intake port to the exhaust port. The magnetic coupling is configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value.

The second vacuum pump exhausts the gas transferred to the exhaust port.

The controller includes a detection section and a revolution control section. The detection section detects a load torque of the drive motor. The revolution control section controls the number of revolutions of the drive motor. The controller increases the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reduces the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.

In the vacuum exhaust device, the second vacuum pump has a function as an auxiliary pump that exhausts gas at a back-pressure of the first vacuum pump. Typically, the exhaust amount of the second vacuum pump is smaller than that of the first vacuum pump. In this regard, the first vacuum pump sets the first and second threshold values for the load torque of the drive motor and controls the number of revolutions of the drive motor in accordance with the magnitude of the detected load torque. Thus, a stable exhausting operation can be achieved without causing the step-out of the magnetic coupling.

According to an embodiment of the present invention, there is provided a method of operating a vacuum pump including a rotor, a drive motor, and a magnetic coupling configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value.

The method includes detecting a load torque of the motor.

The number of revolutions of the drive motor is increased when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value.

The number of revolutions of the drive motor is reduced when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.

In the method of operating a vacuum pump, the first and second threshold values are set for the load torque of the drive motor, and the number of revolutions of the drive motor is controlled in accordance with the magnitude of the detected load torque. Thus, a stable exhausting operation can be achieved without causing the step-out of the magnetic coupling.

Hereinafter, an embodiment of the present invention will be described with reference so the drawings.

FIG. 1 is a schematic configuration diagram showing a vacuum exhaust device according to the embodiment of the present invention. A vacuum exhaust device 10 in this embodiment includes a first vacuum pump 1 and a second vacuum pump 11.

An intake port of the first vacuum pump 1 is connected to a chamber C via a vacuum valve V, and an exhaust port of the first vacuum pump 1 is connected to an intake port of the second vacuum pump 11. The first vacuum pump 1 functions as a main pump that exhausts gas in an inner space of the chamber C and is formed of a mechanical booster pump in this embodiment. On the other hand, the second vacuum pump 11 functions as an auxiliary pump that exhausts gas at a back-pressure of the first vacuum pump 1. The type of the second vacuum pump 11 is not particularly limited, and a rotary pump is used therefor, for example. In addition to the rotary pump, dry pumps such as a diaphragm pump and a scroll pump may be used.

Next, the first vacuum pump 1 will be described in detail.

FIG. 2 is a schematic cross-sectional view showing the first vacuum pump 1. FIG. 3 is a cross-sectional view showing the inner configuration of the pump unit. In each figure, an X-axis direction and a Y-axis direction indicate horizontal directions orthogonal to each other, and a Z-axis direction indicates a vertical direction (direction of gravity) that is orthogonal to those above directions.

The first vacuum pump 1 is formed of a single stage mechanical booster pump. The first vacuum pump 1 includes a pump unit 2, a drive unit 3, and a rotation transmission unit 4.

The pump unit 2 includes a first casing 20 that forms a pump chamber 23. The first casing 20 includes an intake port 201 that communicates with a vacuum chamber (not shown) and an exhaust port 202 that communicates with a pump device (for example, rotary pump) at a subsequent stage. The intake port 201 and the exhaust port 202 communicate with the pump chamber 23. The pump chamber 23 is defined by the first casing 20 and partition wails 24 and 25 that are airtightly attached to both sides of the first casing 20.

The pump unit 2 includes a par of rotors 21 and 22. The rotor 21 and the rotor 22 include a rotation shaft 210 and a rotation shaft 220, respectively, which extend in the Y-axis direction in parallel to each other. The rotors 21 and 22 each have a cross section of a cocoon shape. As shown in FIG. 3, the rotors 21 and 22 are arranged close to each other and accommodated in the pump chamber 23. Small spaces (for example, about 0.02 to 0.04 mm) are held between those rotors 21 and 22, between the rotors 21 and 22 and the first casing 20, and between the rotors 21 and 22 and the partition walls 24 and 25.

The rotation shafts 210 and 220 pass through the partition walls 24 and 25, and one end portions of the rotation shafts 210 and 220 are located in a motor chamber 33 within the drive unit 3. Then, the other end portions of the rotation shafts 210 and 220 are located in a gear chamber 43 within the rotation transmission unit 4.

The drive unit 3 includes a second casing 30 that is airtightly attached to the partition wall 24. The motor chamber 33 is formed within the second casing 30. A bearing 31 and a shaft seal 32 that rotatably support the rotation shafts 210 and 220 are provided on the motor chamber 33 side of the partition wall 24.

The motor chamber 33 communicates with the pump chamber 23 via a first deaeration path P1. Thus, the motor chamber 33 can be deaerated via the first deaeration path P1, and the pressure thereof and a pressure of the pump chamber 23 are made uniform at the operation of the vacuum pump 1. In this embodiment, the first deaeration path 51 is formed of a path that passes through the partition wall 24 in the Y-axis direction.

The drive unit 3 includes a drive motor 35 that rotates the rotation shaft 210 of the rotor 21. The drive motor 35 includes a drive shaft 350 that is fax to the second casing 30 and is coupled to the rotation shaft 210 via a magnetic coupling mechanism 50. The drive motor 35 is formed of a brushless DC (direct current) motor, for example, and the number of revolutions or a rotating speed of the drive shaft 350 is controlled by a controller 60 to be described later.

The magnetic coupling mechanism 50 includes an annular inner-circumferential-side magnet 51 that is fixed to the circumference of the rotation shaft 210 and an annular outer-circumferential-side magnet 52 that is fixed to the circumference of the drive shaft 350. By the magnetic connection of those magnets 51 and 52, the rotation shaft 210 and the drive shaft 350 are coupled to each other.

The inner-circumferential-side magnet 51 is arranged at an outer circumferential portion of a support member 53, which is fixed to the leading end of the rotation shaft 210, and the outer-circumferential-side magnet 52 is arranged at an inner circumferential portion of a support member 54, which is fixed to the drive shaft 350. The inner-circumferential-side magnet 51 and the outer-circumferential-side magnet 52 are opposed to each other via a partition member 55. An edge portion of the partition member 55 is airtightly fixed to an annular convex portion 30 a that is formed on an inner circumferential surface of the second casing 30. The motor chamber 33 in which the inner-circumferential-side magnet 51 is arranged and an air chamber 34 in which the outer-circumferential-side magnet 52 is arranged are partitioned by the partition member 55.

The rotation transmission unit 4 includes a third casing 40 that is airtightly attached to the partition wall 25. The gear chamber 43 is formed within the third casing 40. A bearing 45 and a shaft seal 46 that rotatably support the rotation shafts 210 and 220 are provided on the gear chamber 43 side of the partition wall 25.

The third casing 40 forms the gear chamber 43 that accommodates a gear mechanism. The gear mechanism rotates the rotors 21 and 22 in a synchronized manner in different directions. The gear mechanism includes a synchronous gear 41 that is fixed to the end portion of the rotation shaft 210 and a synchronous gear 42 that is fixed to the end portion of the rotation shaft 220. Thus, when the one rotation shaft 210 rotates about the axis thereof by the driving of the motor 35, a rotational force is transmitted to the other rotation shaft 220 via the synchronous gears 41 and 42. As that time, the rotation shaft 220 is rotated in a direction opposite to a direction in which the rotation shaft 210 is rotated.

Lubricating oil G for lubricating the gear mechanism is retained in the gear chamber 43. Plates 47 that scrape the lubricating oil G are fixed to the leading ends of the synchronous gears 41 and 42 to supply the lubricating oil G to the synchronous gears 41 and 42, the bearing 45, and the like by rotating together with the synchronous gears 41 and 42. Thus, the rotors 21 and 22 can be properly rotated while maintaining relative positions thereof. A window 44 for checking the amount of the lubricating oil G retained in the gear chamber 43 is provided in the third casing 40. A shield 48 is provided in the gear chamber 43 in order to suppress the splatter of the lubricating oil G due to the rotation of the synchronous gears 41 and 42. The shield 48 has a substantially flat shape and is attached to the partition wall 25 so as to cover the upper portions of the synchronous gears 41 and 42.

The gear chamber 43 communicates with the motor chamber 33 via a second deaeration path P2. Thus, the gear chamber 43 can be deaerated via the second deaeration path P2, and the pressure thereof and pressures of the motor chamber 33 and the pump chamber 23 are made uniform at the operation of the vacuum pump 1.

In this embodiment, the second deaeration path P2 allows the gear chamber 43 to communicate with the motor chamber 33 via the third casing 40, the partition wall 25, the first casing 20, and the partition wall 24. The second deaeration path P2 is mainly formed of a main path portion P21 that passes through the first casing 20 and the partition walls 24 and 25 in the Y-axis direction and a communication path portion P22 formed in the third casing 40. Note that the main path portion P21 and the motor chamber 33 may be connected to each other by forming a similar communication path portion also in the second casing 30.

The first vacuum pump 1 further includes the controller 60. The controller 60 includes a detection section 61 that detects a load torque of the drive motor 35 and a revolution control section 62 that controls the number of revolutions of the drive motor 35. Typically, the controller 60 is formed of a computer including an arithmetic section, a memory, and the like and may be integrally formed with the drive unit 3, for example.

The detection section 61 detects a load torque of the drive motor 35 that rotates the rotor 21 via the magnetic coupling mechanism 50. A detection method for a load torque is not particularly limited and a known method can be adopted. For example, a load torque of the drive motor 35 can be detected by measuring a voltage between both ends of a detection coil connected in series to an exciting coil wound into a stator of the drive motor 35.

The revolution control section 62 controls the number of revolutions of the drive motor 35. A control, method for the number of revolutions is not also particularly limited. Typically, the number of revolutions is controlled by controlling an induced electromotive force of the motor. In this embodiment, the revolution control section 62 includes an inverter. The form of the inverter is not also particularly limited, and a PWM (pulse-width modulation method) is adopted, for example.

The controller 60 controls the number of revolutions of the drive motor 35 based on the output of the detection section 61. Specifically, when the load torque of the drive motor 35 is equal no or smaller than a second threshold value (Th2) that is smaller than a first threshold value (Th1), the controller 60 increases the number of revolutions of the drive motor 35. Further, when the load torque of the drive motor 35 exceeds the second threshold value (Th2) and is equal to or smaller than the first threshold value (Th1), the controller 60 reduces the number of revolutions of the drive motor 35.

Here, the first threshold value (Th1) refers to a maximum drive torque of the drive motor 35, at which the rotor 21 can be rotated without causing a step-out of the magnetic coupling mechanism 50. The step-out of the magnetic coupling mechanism 50 means that a magnetic connection between the inner-circumferential-side magnet 51 and the outer-circumferential-side magnet 52 is released and refers to a status in which the drive shaft 350 of the drive motor 35 and the rotation shaft 210 of the rotor 21 cannot be rotated in a synchronized manner.

The first threshold value (Th1) is determined in consideration of a magnetic connection force of the magnetic coupling mechanism 50, an exhaust amount [Pa/m³/s] of the first vacuum pump 1, an exhaust amount [Pa/m³/s] of the second vacuum pump 11, an operating pressure of the first vacuum pump 1, and the like. Specifically, since the load torque (step-out torque) at which a step-out occurs varies depending on the number of revolutions of the motor, a back-pressure (pressure on the exhaust port side) of the pump, and the like, the first threshold value (Th1) is set in consideration of the various conditions described above. In this embodiment, the first threshold value (Th1) is 0.8 N·m.

The second threshold value (Th2) is set to be an appropriate value smaller than the first threshold value (Th1). When the load torque of the drive motor 35 is equal to or smaller than the second threshold value (Th2), the controller 60 increases the number of revolutions of the drive motor 35, and when the load torque exceeds the second threshold value (Th2) and is equal to or smaller than the first threshold value (Th1), the controller 60 reduces the number of revolutions of the drive motor 35. Specifically, in this embodiment, the number of revolutions of the drive motor 35 is reduced with the second threshold value (Th2) smaller than the first threshold value (Th1) being as a reference. Thus, the step-out of the magnetic coupling mechanism 50 is reliably prevented and a stable exhausting operation is achieved. The second threshold value (Th2) can be appropriately set, and in this embodiment, the second threshold value (Th2) is 0.55 N·m.

The second threshold value (Th2) can be a rated torque of the drive motor 35. Thus, the drive motor 35 can be driven efficiently, and the reduction in power consumption can also be achieved. Note that the second threshold value (Th2) is not limited to be set to the same value as the rated torque of the drive motor 35. For example, the second threshold value (Th2) may be set to a value slightly larger than the rated torque described above in consideration of fluctuation of the load torque of the rated number of revolutions.

Further, when the load torque of the drive motor 35 exceeds the first threshold value (Th1), the controller 60 puts the drive motor 35 into a free running state. When the detected load torque exceeds the first threshold value, the magnetic coupling has a high possibility of causing the step-out. In this regard, in the vacuum pump described above, when the load torque of the drive motor exceeds the first threshold value, the drive motor 35 is put into a free running state where the excitation of the drive motor is blocked, and the drive motor is rotated through inertia. Thus, the step-out state of the magnetic coupling can be resolved early.

Next, an operation of the vacuum exhaust device 10 in this embodiment will be described.

Referring to FIG. 1, the inside of the chamber C is at atmospheric pressure, and the vacuum valve V is opened. In this state, the first vacuum pump 1 and the second vacuum pump 11 are simultaneously driven.

In the first vacuum pump 1, the rotation shaft 210 rotates together with the drive shaft 350 via the magnetic coupling mechanism 50 by the operation of the motor 35, and thus the rotor 21 rotates within the pump chamber 23. Further, a rotational force of the rotation shaft 210 is transmitted to the rotation shaft 220 of the rotor 22 in the rotation transmission unit 4. Thus, the rotor 22 is synchronized with the rotor 21 and rotates in a direction opposite to the direction in which the rotor 21 rotates. By the rotation of those rotors 21 and 22, the pump unit 2 performs a predetermined pump operation in which gas taken in from the intake port 201 is exhausted toward the exhaust port 202.

At that time, the controller 60 rotates the drive motor 35 at a rotational torque equal to or smaller than the first threshold value (Th1) and transmits a rotational force to the rotor 21 via the magnetic coupling mechanism 50. The first threshold value (Th1) corresponds to a rotational torque at which the drive motor 35 and the rotor 21 can be rotated in a synchronized manner without causing the step-out of the magnetic coupling mechanism 50.

The motor chamber 33 and the gear chamber 43 are depressurized with the reduction of the pressure of the pump chamber 23 via the first and second deaeration paths P1 and P2. Thus, the difference in pressure between the pump chamber 23 and the motor chamber 33 and gear chamber 43 that are adjacent to the pump chamber 23 becomes smaller, and thus degradation of pump performance due to the leakage of the pump chamber 23 is prevented.

The second vacuum pump 11 is always driven when the first vacuum pump 1 is driven. The second vacuum pump 11 exhausts gas at a back-pressure of the first vacuum pump 1, that is, gas transferred to the exhaust port 202.

In an early stage of the activation of the vacuum exhaust device 10, the first vacuum pump 1 exhausts the chamber C under atmospheric pressure. For that reason, the exhaust port 202 of the first vacuum pump 1 may reach a pressure equal to or larger than the atmospheric pressure. At that time, the gas within the pump chamber 23 flows backwardly to the motor chamber 33. However, since the partition member 55 of the magnetic coupling mechanism 50 airtightly partitions the motor chamber 33 and the drive motor 35, the lubricating oil for the shaft seal and the like does not flow into the drive motor 35. Therefore, the lubricating oil is prevented from being leaked to the outside of the pump unit.

On the other hand, in an early stage of the activation of the vacuum exhaust device 10, since the back-pressure of the first vacuum pump 1 is relatively large, a rotational load of the rotor 21 exceeds a rotational load of the drive motor 35, which easily causes the step-out of the magnetic coupling mechanism 50. In this regard, the controller 60 controls the number of revolutions of the drive motor 35 as follows.

FIG. 4 is a control flow of the drive motor 35 by the controller 60. FIG. 5 is a timing chart showing an example of temporal changes in load torque and the number of revolutions of the drive motor 35.

The controller 60 measures a load torque of the drive motor 35 based on the output of the detection section 61 (Step 1). Next, in the case where the measured load torque is equal to or larger than a third threshold value (Th3) and equal to or smaller than the second threshold value (Th2), the controller 60 executes control of increasing the speed of the drive motor 35, that is, control of increasing the number of revolutions (Steps 2, 3, and 4). Here, the third threshold value (Th3) corresponds to a value that is smaller than the second threshold value (Th2) and larger than a load torque detected when the magnetic coupling mechanism 50 causes a step-out. The value of the third threshold value (Th3) is not particularly limited and is 0.13 N·m, for example.

The control of increasing the number of revolutions is executed when the load torque of the drive motor 35 is equal to or larger than the third threshold value (Th3) and equal to or smaller than the second threshold value (Th2), and thus the exhaust amount of the first vacuum pump 1 can be increased while preventing the step-out of the magnetic coupling mechanism 50. In this embodiment, the number of revolutions of the drive motor 35 is controlled in the range of from 0 to 3,500 r.p.m.

In FIG. 5, sections D1 and D2 correspond to a period from the start of activation of the drive motor 35 to the attainment of a maximum number of revolutions. At this point in time, the load torque of the drive motor 35 does not reach the second threshold value (Th2), and therefore the drive motor 35 is driven at a maximum number of revolutions.

On the other hand, the second vacuum pump 11 has an exhaust amount smaller than that of the first vacuum pump 1, and thus the back-pressure of the first vacuum pump 1 gradually increases and along with the increase, the load torque of the drive motor 35 also increases. Then, in the case where the load torque of the drive motor 35 exceeds the second threshold value (Th2) and is equal to or smaller than the first threshold value (Th1), the control of reducing the number of revolutions of the drive motor 35 is executed (Steps 2, 5, and 6, section D3). Thus, the exhausting operation by the rotation of the rotor 21 can be stably continued while preventing the step-out of the magnetic coupling mechanism 50.

Note that when the load torque of the drive motor 35 exceeds the first threshold value (Th1), the controller 60 determines that the drive motor 35 is overloaded, and then issues an error signal as necessary and stops the drive motor 35 (Step 8).

When the load torque reaches a value equal to or smaller than the second threshold value (Th2) by the control of reducing the number of revolutions of the drive motor 35, the controller 60 executes again the control of increasing the number of revolutions (Steps 2 to 4, section D4). Hereinafter, the execution of the same control as the control described above allows the chamber 1 to be exhausted by the first and second vacuum pumps 1 and 11 (sections D5 and D6).

A section D7 indicates a period in which a step-out of the magnetic coupling mechanism 50 is caused at a time of the control of reducing the number of revolutions of the drive motor 35. The controller 60 determines that the step-out is caused when the load torque of the drive motor 35 is equal to or smaller than the third threshold value (Th3), stops supply of power to the drive motor 35, and puts the drive shaft 350 into a free running state (Steps 3 and 7). Thus, the step-out state of the magnetic coupling mechanism 50 is resolved early. After that, the control of increasing the number of revolutions of the drive motor 35 is executed again so that the exhausting operation of the chamber 1 is resumed. After the chamber C reaches a target pressure, the controller 60 continues driving the drive motor 35 such that the pressure of the chamber C is maintained to be the target pressure. Note that when the operation of the pump is stopped, the controller 60 stops supply of power to the drive motor 35 (section D8).

As described above, according to this embodiment, the number of revolutions is controlled in accordance with the load torque of the drive motor 35. Thus, the exhausting operation can be continued while preventing the step-out of the magnetic coupling mechanism 50. Thus, the chamber C can reach the target pressure early. Further, the chamber C can be exhausted from the atmospheric pressure to the target pressure by the first vacuum pump 1.

FIG. 6 shows results of an experiment of a change in the number of revolutions of the drive motor 35 from the start of activation of the first vacuum pump 1 to the attainment of the target pressure. FIG. 6 also shows temporal changes of a pressure (P1) of the intake port 201 and a pressure (P2) of the exhaust port 202. In the measurement, the vacuum chamber C having the interior volume of 20 L is used. As shown in FIG. 6, according to this embodiment, a stable exhausting operation can be achieved without causing the step-out of the magnetic coupling mechanism 50.

Hereinabove, the embodiment of the present invention has been described, but the present invention is not limited thereto and can be variously modified based on the technical idea of the present invention.

For example, in the above embodiment, the first to third threshold values (Th1 to Th3) are set for the load torque of the drive motor 35 when the number of revolutions of the drive motor 35 in the first vacuum pump 1 is controlled. However, the magnitude of the threshold values and the number of threshold values to be set are not limited to the above example and may be appropriately changed.

Further, in the above embodiment, the mechanical booster pump is used as the first vacuum pump 1, but the first vacuum pump 1 is not limited thereto. The present invention is applicable to other dry vacuum pumps such as a multistage roots-type pump and a scroll pump.

DESCRIPTION OF REFERENCE NUMERALS

1 first vacuum pump

2 pump unit

3 drive unit

10 vacuum exhaust device

11 second vacuum pump

21, 22 rotor

23 pump chamber

25 drive motor

50 magnetic coupling mechanism

51 inner-circumferential-side magnet

52 outer-circumferential-side magnet

55 partition member

60 controller

61 detection section

62 revolution control section

201 intake port

202 exhaust port 

1. A vacuum pump, comprising: a pump unit including a pump chamber including an intake port and an exhaust port, and a rotor that is arranged in the pump chamber and transfers gas from the intake port to the exhaust port; a drive unit including a motor chamber adjacent to the pump chamber, and a drive motor that is arranged in the motor chamber and rotates the rotor; a magnetic coupling including a partition member that airtightly partitions the pump chamber and the motor chamber, a first magnet attached to the rotor, and a second magnet that is attached to the drive motor and is magnetically connected to the first magnet via the partition member, the magnetic coupling being configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value; and a controller including a detection section that detects a load torque of the drive motor, and a revolution control section that controls the number of revolutions of the drive motor, the controller increasing the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reducing the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than toe first threshold value.
 2. The vacuum pump according to claim 1, wherein the controller puts the drive motor into a free running state when the load torque exceeds the first threshold value.
 3. The vacuum pump according to claim 1 or claim 2, wherein the second threshold value is a rated torque of the drive motor.
 4. A vacuum exhaust device, comprising: a first vacuum pump including a pump chamber including an intake port and an exhaust port, a rotor that is arranged in the pump chamber and transfers gas from the intake port to the exhaust port, a drive motor, and a magnetic coupling configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value; a second vacuum pump that exhausts the gas transferred to the exhaust port; and a controller including a detection section that detects a load torque of the drive motor, and a revolution control section that controls the number of revolutions of the drive motor, the controller increasing the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reducing the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value.
 5. A method of operating a vacuum pump including a rotor, a drive motor, and a magnetic coupling configured to transmit a rotational force of the drive motor to the rotor at a rotational torque equal to or smaller than a first threshold value, the method comprising: detecting a load torque of the motor; and increasing the number of revolutions of the drive motor when the load torque is equal to or smaller than a second threshold value that is smaller than the first threshold value and reducing the number of revolutions of the drive motor when the load torque exceeds the second threshold value and is equal to or smaller than the first threshold value. 